The "Cake Room Secret Ending" legend is an urban legend revolving around the 2007 first-person puzzle game Portal.
Description
Throughout the game, the antagonistic AI GLaDOS tempts you with a chocolate cake should you complete your various tests in special test chambers. At the game's end, the cake is finally shown but is unobtainable. This led to rumors that players could access the room this ending cutscene takes place in and unlock a special ending. While the room can be accessed via cheating and clipping through the walls, fans speculated that a more legitimate method was available.
According to the rumors, players must reach chamber 19 and progress until they reach a large tall room with various turrets situated in small alcoves on the walls. Players must take out all of the turrets and use their portal gun to reach the lowest bridge and head into the control room. Then, players must fire both portals at a specific spot on the wall using a technique known as portal-bumping, which creates a singular tunnel on sufficiently thin walls. Using this technique, players can shoot a portal on top of the cake room, which lies outside the normal map geometry. Done correctly, the player should be inside the cake room with the infamous chocolate cake.
A companion cube lies inside the cake room. Take the companion cube and place it on top of the cake. Reversing the above process will allow the player to return to the normal game map and complete the game as normal. According to the legend, when the cake room ending cutscene plays, the robot arm that snuffs out the cake's candle will be blocked by the companion cube sitting atop the cake, triggering the alternate ending. Unfortunately, no alternate cutscene exists. The game is unable to proceed further due to the normal cutscene being unable to play.